This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The bacterial response to osmotic fluctuations in the external environment involves a highly complex and integrated network of physiological and genetic changes. In bacteria such as Escherichia coli, the key response is the "salt out strategy" that requires the biosynthesis and/or transport of low molecular weight organic solutes, called osmolytes or compatible solutes, into the cell cytoplasm. These compatible solutes, generally amino acids or their derivatives and carbohydrates, can reach high concentrations without interrupting cellular functions. Vibrio parahaemolyticus is a moderately halophilic Gram-negative bacterium and a natural inhabitant of estuarine and marine environments. Because V. parahaemolyticus inhabits the interface between both high and low salinity environments, it must adapt to changes in osmolarity of the external environmental, which is vital to its ability to grow and survival. The genes, proteins and mechanisms by which V. parahaemolyticus cope with and respond to osmotic challenges are unknown. We identified by bioinformatic analysis a total of six uncharacterized compatible solute transporters on the genome, which is double the number found in other Vibrio species and in bacteria in general. Whether each of these transport systems can uptake one or several compatible solutes in response to increasing osmotic pressure is unknown. Furthermore, these transporters may also be required for adaptation to additional stresses and/or osmolyte switiching under different conditions. Our overall hypothesis is that these compatible solute transporters are required for osmoadaptation, osmosensing and regulation as well as responding to other stresses such as low temperature and acid stress. Our first objective is to demonstrate compatible solute uptake by each of these transporters. Our second objective will determine whether each transport has different affinities for a range of solutes. Our third objective will examine using gene expression profiling the role of these transporters in temperature and acid stress responses.